JPH0550198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital speaker that is applied to a reproducing device for PCM (Pulse Code Modulation) audio signals.

BACKGROUND TECHNOLOGY AND PROBLEMS In recent years, in the field of audio equipment, the S/N ratio has been improved and the dynamic range expanded during the recording, playback, and amplification stages of audio signals by converting audio signals into PCM and handling them. ,
PCM conversion of audio signals is being actively adopted due to various possible benefits such as reduction in non-linear distortion.

By the way, in order to digitize an audio signal waveform, which is an analog signal, according to the sampling theorem, two of the highest frequencies contained in the audio signal are
It is known that it is sufficient to perform sampling at twice the repetition frequency and convert the sampled value into a binary code, but in order to recover the original audio signal from this binary code, it is necessary to It is necessary to provide a D/A conversion function to the path. For this reason, digital speakers have been developed that perform D/A conversion directly at the electro-acoustic conversion stage.

However, in conventional digital speakers, as shown in Figure 1, a sounding section (electro-acoustic converter) for each bit digit has a diaphragm area proportional to the weight of each bit digit of the parallel PCM digital signal. ) 1 to 6, and each sound generating section generates a pulse sound with a level proportional to the weight of each bit digit, which is added and synthesized in the sound field (space),
Performs digital-to-analog conversion to reproduce analog sound.

However, since the sounding units 1 to 6 responsible for each bit digit to generate an acoustic output representing the weight of each bit digit are not completely the same, there are differences in sound pressure frequency characteristics, phase characteristics, and sound pressure characteristics between each sounding unit. This causes an error in propagation time, making it difficult to perform correct D/A conversion (reproduction).

In addition, the sound generation units 1 to 6, which are electric-acoustic conversion units,
If the weights were determined individually, it was impossible to reproduce PCM signals with different code systems (weights).
Furthermore, since the sound generating sections responsible for each bit are unevenly distributed (concentrated in one place), correct D/A conversion is difficult.

Purpose of the Invention In view of these conventional problems, the present invention
PCM signals can be D/A converted correctly, and even PCM signals with different code systems (weights) can be D/A converted by changing the weights according to the code system, which improves playback quality and is easy to manufacture.・The purpose is to provide speakers.

Summary of the Invention The digital speaker according to the present invention has a plurality of fan-shaped diaphragms having the same area arranged radially to form a substantially circular shape, and has a vibration area proportional to the weight of each bit digit of a parallel PCM signal. The diaphragms are selectively connected in parallel and grouped so that the diaphragms in each group are distributed at approximately equal intervals. With this configuration, extremely accurate D/A conversion performance is obtained.

Embodiments Examples of the present invention will be described below with reference to the drawings.

FIG. 2 shows a main part of an embodiment of a digital speaker according to the present invention, and FIGS. 2A and 2B are a front view of a piezoelectric driver attached to a horn, and a sectional view taken along the line A--A in FIG. In Fig. 2, 11 is a diaphragm formed of a fan-shaped piezoelectric element.
Each diaphragm 11 is fixed at a peripheral portion corresponding to its inner diameter and outer diameter with fixing rings 12 and 13.
Adjacent parts are connected by a viscoelastic body 14 so that the vibrating bodies become independent of each other. Each diaphragm 11 is arranged in a disc shape (radially), and the entire vibration plate 11 is arranged in a disc shape (radially).
As shown in Figure b, it is formed into a dome shape. Reference numeral 15 denotes electrodes made of thin metal foils that are adhered or vapor-deposited on the front and back surfaces of the diaphragm 11.

As is well known, the diaphragm 11 made of such a piezoelectric element expands and contracts in accordance with the voltage value by applying a voltage to the electrodes 15, 15 formed on the front and back sides, thereby generating sound pressure. However, the diaphragm 11
Since the end faces of are fixed by fixing rings 12 and 13, the expansion and contraction movement is in the thickness direction shown by the dotted line, and a vibration surface is formed. Therefore, a digital speaker is formed by using such a diaphragm 11 as a horn speaker driver and driving each diaphragm 11 with a binary code of parallel PCM digital signals as follows.

That is, in the present invention, one diaphragm 11 and the electrodes 15 on both sides constitute one unit of sounding body 16, and each sounding body (subdivided small electro-acoustic transducer) 16 is driven independently. Furthermore, the same pulsed sound with the same sound pressure frequency characteristics and phase characteristics is emitted. Furthermore, here, as shown in FIG.
The sounding bodies 16 are grouped every third into one set,
(MSB-2) bit means that every seven sounding bodies 16 are grouped together as one set, so the sounding section 17 of each bit digit generates a number of sounding bodies 16 in proportion to the weight of that bit digit. They are connected in parallel to form one group. Moreover, the sounding bodies 16 constituting each group are distributed at substantially equal intervals. Note that one sounding body 16 is not used redundantly between each group. Therefore, the total number of sounding elements 16 is required to be equal to the sum of the weights of each bit digit of the PCM signal.

Therefore, each of the sound generating units (electro-acoustic converters) 17 of each bit digit grouped in this manner has the characteristics of each electric-acoustic converter 17 (electrical characteristics seen from the drive system and electric-acoustic converters as a sounding body). acoustic conversion characteristics)
Since there is no difference between the two and the sound sources are not unevenly distributed, the characteristics as an electro-acoustic converter having a D/A conversion function are extremely good.

FIG. 3 shows a driving circuit for one bit digit (eg, MSB). In Figure 3, the input terminal
When a pulse input is supplied to I ₁ , the transistor
T ₁ and T ₂ are turned on, and the terminal voltage of resistor R ₁ becomes MSB.
Each sounding body 16 that constitutes the sounding section 17, 17a of the digit
a (in FIG. 2, the sounding bodies 16 are distributed approximately evenly in a radial manner, that is, here, for example, every other sounding body 16 is disposed), and each diaphragm 11 constituting the sounding body 16a is vibrated. In addition, +Vcc
is the power source. Regarding other bit digits, one group of sounding elements 16 constituting the bit digits are driven in parallel as shown in FIG.

Therefore, there are n sound generating units 17 corresponding to n bits.
When a parallel PCM signal is added to
The radially distributed sounding bodies 16 constituting each sounding section of each bit digit are all driven, and each diaphragm 11 constituting each driven sounding body 16 is vibrated to emit a pulse sound. Then, by adding and synthesizing these pulse sounds in a spatial sound field, D/A conversion is performed and analog sound is reproduced.

In this embodiment, although the case of binary code is mentioned as the coding method of the parallel PCM signal, the present invention is not limited to this and can be similarly applied to any coding method. In this case, the electro-acoustic transducer (sounding body) is
is grouped into an electro-acoustic transducer (sounding part)
is formed. Therefore, in order to apply it to another chord system, it is sufficient to simply change the number of combinations of sounding bodies.

Effects of the Invention The use of the present invention provides the following various effects.

(1) Even though the area ratio of the diaphragm representing each bit digit of the parallel PCM signal is proportional to the weight of the bit digit, the sounding section of each bit digit is a minute unit sounding body. Since the devices are grouped and connected in parallel in a number corresponding to the vibration area proportional to the weight of the bit digit, the sounding section of each bit digit depends on the electric-acoustic conversion performance and the electric power of the sounding section from the perspective of the drive system. characteristics are uniform. Therefore, good D/A conversion performance can be obtained when reproducing audio signals.

(2) Since the unit sounding bodies that make up each bit digit are evenly distributed, the sound source is not biased. Therefore, when reproducing an audio signal, D/
A conversion can be performed correctly, thereby improving the reproduction quality of audio signals.

(3) Even if the coding method (weight) of the PCM signal changes, the number of unit sounding elements to be driven can be freely changed, so any coding method can be used.
It can also handle PCM signals.

(4) There is no need to form a large-area sounding body;
Easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a main part of a conventional digital speaker, and FIGS. 2a and 2b are front views showing main parts of an embodiment of a digital speaker according to the present invention, and -A sectional view and FIG. 3 is a circuit diagram showing an example of the drive circuit of the sounding section. In addition, in the symbols used in the drawings, 16...
Sounding body (electrical-acoustic converter), 17... Sounding unit (electrical-acoustic converting unit).

Claims (1)

[Scope of Claims] 1. A plurality of fan-shaped diaphragms each having the same area, and a signal of a predetermined bit digit of a parallel PCM signal that is attached to each of the diaphragms and drives the diaphragms. Each of the diaphragms is arranged radially in a substantially circular shape, and each diaphragm has a number of diaphragms proportional to the weight of each bit digit of the parallel PCM signal connected in parallel. a plurality of groups, the diaphragms in each group being distributed at substantially equal intervals.